Pelvic Avulsion Fractures

Definition: Pelvic avulsion fractures are injuries where a muscle-tendon unit avulses its apophyseal attachment from the pelvis. They occur almost exclusively in adolescents due to the relative weakness of the unfused apophysis compared to the muscle-tendon unit.

Epidemiology:

• Age: 14-17 years (before apophyseal closure).
• Sex: Males greater than Females.
• Sports: Sprinting, Soccer, Gymnastics, Hurdling, Baseball.
• Bilaterality: Rare.

Common Sites:

1. ASIS (Anterior Superior Iliac Spine): Sartorius.
2. AIIS (Anterior Inferior Iliac Spine): Rectus Femoris (Straight head).
3. Ischial Tuberosity: Hamstrings (Semimembranosus, Semitendinosus, Biceps Femoris long head).
4. Iliac Crest: External Oblique, Internal Oblique, Transversus Abdominis.
5. Lesser Trochanter: Iliopsoas.

Apophyseal Anatomy:

• Apophysis: Secondary ossification center for muscle attachment.
• Weakness: Cartilaginous growth plate is weaker than bone, muscle, or tendon.
• Closure: Apophyses fuse in late adolescence (17-25 years).

Mechanism:

• Sudden Contraction: Explosive muscle contraction against resistance.
• Eccentric Load: Muscle lengthening under load (e.g., hurdle).
• Result: Apophysis avulses before muscle or tendon fails.

Site-Specific Mechanisms:

• ASIS (Sartorius): Sprinting (hip extension with knee flexion).
• AIIS (Rectus Femoris): Kicking (hip flexion with knee extension).
• Ischial Tuberosity (Hamstrings): Hurdles, Splits, Waterskiing.
• Iliac Crest: Twisting, Throwing.

History:

• Mechanism: Sudden pop/pain during sprinting, kicking, or jumping.
• Sport: Sprinting, Soccer, Gymnastics.
• Age: Adolescent (13-17).

Physical Examination:

• Tenderness: Point tenderness over avulsion site (ASIS, AIIS, IT, Iliac Crest).
• Swelling/Bruising: Variable.
• Weakness: Weakness of the involved muscle (Hip flexion, Hamstrings).
• Gait: Antalgic.
• ROM: Painful with stretch of involved muscle.

Imaging:

1. X-ray (AP Pelvis): Compare to contralateral side. Look for displaced fragment.
2. CT: If X-ray unclear. Quantify displacement.
3. MRI: Rarely needed. For soft tissue assessment or chronic cases.

Key Findings:

• ASIS Avulsion: Fragment displaced inferolaterally.
• AIIS Avulsion: Fragment displaced inferiorly.
• Ischial Tuberosity: Fragment displaced inferiorly (by hamstrings).
• Iliac Crest: Multiple small fragments (apophysis strips).

• Crutches: 2-4 weeks.
• ROM: Early gentle ROM.
• Strengthening: Week 4-6 progressive.
• Return to Sport: 12-16 weeks (post-surgery).

• Conservative: 90%+ return to full sport.
• Surgical (IT): Good outcomes with ORIF.
• Long-term: No significant issues if managed appropriately.

There are no randomised trials and no formal society guideline for pelvic apophyseal avulsions; practice is built on retrospective series and expert consensus. Key unsettled questions:

• Operative displacement threshold. Commonly quoted cut-offs range from over 15mm (Ghanem) to over 20mm (Schuett nonunion data) to "over 2cm" as a teaching round number. The figure is a guide, not a rule — there is no level I/II evidence defining a single threshold.
• Which site predominates. Older radiographic series report ischial tuberosity as the most common site (Rossi), whereas the largest modern imaging-era series reports AIIS as most common (Schuett, 49%). Both are quotable; the discrepancy reflects era, referral pattern and imaging access.
• Surgery vs conservative for the displaced ischial tuberosity. Surgery offers higher return-to-pre-injury sport and lower nonunion but adds heterotopic ossification and operative risk (Calderazzi). The trade-off is individualised by athletic demand, displacement and fragment size.
• Acute fixation vs delayed/secondary surgery. Many displaced injuries can be treated conservatively first, reserving fixation/excision for symptomatic nonunion — but this risks a harder secondary operation through scar.
• Role of MRI/ultrasound. Useful for purely cartilaginous avulsions in the young (radiographically occult) and for tumour-mimic reassurance, but routine advanced imaging is not justified when the radiograph and history are clear.

Global epidemiology

• Predominantly adolescents aged 11-17 with open apophyses; male predominance (around 76% in the largest series).
• Sport profile is region-driven: soccer and gymnastics dominate in European data (Rossi), while sprinting/running and kicking dominate North American data (Schuett). Track and field, dance, martial arts and racquet sports also feature.
• Overall a benign, self-limiting injury — roughly 97% are managed non-operatively with excellent outcomes.

Guidance across societies (no dedicated guideline exists)

Registry note. Pelvic avulsion fractures are not tracked by arthroplasty/implant registries (NJR, AJRR, AOANJRR, SHAR) — these are non-implant, paediatric soft-tissue-bone injuries, so registry survivorship data do not apply.

High- vs limited-resource practice

• Well-resourced settings: ready radiographs, CT to quantify displacement, MRI for occult cartilaginous avulsion or tumour-mimic reassurance, and access to surgical fixation/arthroscopic subspine decompression when indicated.
• Limited-resource settings: diagnosis rests on a single AP pelvis radiograph and clinical examination; conservative management is the near-universal default and yields good results, with the main risk being missed diagnosis rather than under-operating.